1. Field of the Invention
The present invention relates to ball grid array ("BGA") packages and methods of testing or otherwise evaluating BGA packages. In particular, the present invention relates to test interposers that may be disposed between a BGA semiconductor device and a carrier substrate with which the BGA semiconductor device is in electrical communication. The present invention also includes BGA packages that include the interposer sandwiched between a BGA semiconductor device and a carrier substrate. The present invention also relates to methods of testing or otherwise evaluating BGA packages by employing the interposer of the invention.
2. Background of the Related Art
Ball grid array ("BGA") packages typically include a semiconductor die that has bond pads disposed over an active surface thereof, rather than merely proximate a periphery thereof. Thus, the bond pads of BGA semiconductor dice may be disposed across the active surfaces of the BGA semiconductor dice at an increased density relative to the bond pads disposed on conventional semiconductor dice with peripherally located bond pads. Therefore, BGA semiconductor dice may have smaller dimensions or an increased number of bond pads relative to the dimensions or number of bond pads of conventional semiconductor dice.
BGA packages typically include a carrier substrate to which the BGA semiconductor dice are flip-chip bonded, TAB bonded, or otherwise invertedly secured. Thus, the footprint of the terminals of the BGA carrier substrate corresponds substantially to the footprint of bond pads on an inverted BGA semiconductor die. As the use of BGA packages eliminates conventionally employed wire bonds that typically extend past the periphery of a semiconductor die to establish an electrical connection between the semiconductor die and a carrier substrate, the circuit density of the carrier substrate may be increased.
In order to test or otherwise evaluate the characteristics of the electrical signals transmitted to and from BGA packages, some manufacturers have employed specially designed test substrates in place of the carrier substrate. These test substrates may include test pads that extend from the circuitry of the test substrate. The use of such test substrates is, however, somewhat undesirable in that the circuitry of the test substrate does not accurately represent the circuitry of a corresponding carrier substrate to be employed in production of the BGA package. For example, the test substrate and production carrier substrate may have different circuit patterns, different circuit lengths, and different circuit densities. Thus, the circuits of the test substrate could consume more "real estate" on the test substrate than the circuits of a production carrier substrate, the circuits of the test substrate may not be optimally electrically routed for production, or the electrical characteristics of the test substrate may otherwise differ substantially from the electrical characteristics of a corresponding production carrier substrate.
Another approach to testing BGA packages involves the use of an interposer with test posts extending upwardly from the periphery of the interposer around the BGA semiconductor die. As each of the upwardly extending test posts of such an interposer would have to be electrically optimized, the electrical characteristics of a BGA package including such an interposer would not accurately represent the electrical characteristics of a similar BGA package without the interposer. Moreover, these upwardly extending test posts may act as antennas and may, therefore, interfere with the electrical properties of the BGA package or of any proximate circuit traces or other electrical components. Test interposers that include such upwardly extending test posts are also undesirable from the standpoint that the test posts may increase the overall height of BGA packages including the interposer and may, therefore, decrease the usefulness of the test interposer in production-level BGA packages (i.e., BGA packages with this type of interposer may not be salable).
Accordingly, there is a need for an interposer that may be employed to test or evaluate the electrical characteristics of signals transmitted to and from a BGA semiconductor die, that may be incorporated into a salable BGA package, and that will not interfere substantially with the electrical characteristics of the BGA package or any proximate electrical componentry.